Mixing plate providing reductant distribution

ABSTRACT

A reductant mixing system having injector and mixing plate positioned within mixing canister is disclosed. Injector discharges reductant directly into vehicle exhaust gases. Mixing plate effects turbulence to mix gases for NO reduction. Mixing plate includes plurality of arms each having surface area and extending from center of plate, barrier region defined by collective surface areas of arms and substantially centered for diverting fluid flow outward, and first and second cut-outs, which allow the gases diverted by barrier region to pass mixing plate into adjacent canister of exhaust treatment system. Each of the first cutouts is defined by outer edge between adjacent arms, and second tier of cut-outs defined by inner edge proximate end of each arm.

TECHNICAL FIELD

The present device relates to an ammonia mixing system for a vehicle exhaust after-treatment system. Specifically, the device relates to a mixing plate combined with an ammonia gas injector for effecting NOx reduction in a vehicle exhaust after-treatment system.

BACKGROUND

Compression ignition engines provide advantages in fuel economy, but produce both NO_(x) and particulates during normal operation. New and existing regulations continually challenge manufacturers to achieve good fuel economy and reduce the particulates and NO emissions. Lean-burn engines achieve the fuel economy objective, but the high concentrations of oxygen in the exhaust of these engines yields significantly high concentrations of NO_(x) as well. Accordingly, the use of NO_(x) reducing exhaust treatment schemes is being employed in a growing number of systems.

One such system is the direct addition of a reducing agent or reductant, such as ammonia gas, to the exhaust stream. It is an advantage to deliver ammonia directly into the exhaust stream in the form of a gas, both for simplicity of the flow control system and for efficient mixing of the reducing agent, ammonia, with the exhaust gases. The direct use of ammonia also eliminates potential difficulties related to blocking of the dosing system, which may be caused by precipitation or impurities, e.g., in a liquid-based urea solution. In addition, an aqueous urea solution cannot be dosed at a low engine load since the temperature of the exhaust line would be too low for complete conversion of urea to ammonia (and CO₂).

A couple specific challenges with the direct injection of ammonia relate to dispersion and mixing of the reducing agent with the hot exhaust gases. The dispersion issue considers how to deliver or spread ammonia to the greatest volume of flowing exhaust, while the mixing issue questions how to create the most homogenous mixture of exhaust and ammonia to facilitate the NOx reduction reaction.

Thus, the present system provides both a device for adequately dispersing and sufficiently mixing a reductant, including ammonia into an exhaust gas stream of a vehicle. These and other problems are addressed and resolved by the disclosed system and method of the present application.

SUMMARY

There is disclosed herein a device which avoids the disadvantages of prior devices while affording additional structural and operating advantages.

Generally, a reductant mixing system comprises an injector and a mixing plate positioned within a mixing canister or chamber. While the injector discharges reductant, such as ammonia gas directly into the vehicle exhaust gases, the mixing plate effects turbulence to facilitate mixing of the gases to optimize the NOx reduction reaction.

In an embodiment, the mixing plate comprises a plurality of arms each having a surface area and extending from a center of the plate, a barrier region defined by the collective surface areas of the arms and substantially centered on the center and effective for diverting fluid flow outward, and first and second tier cut-outs, which allow the mixing gases diverted by the barrier region to pass the mixing plate into an adjacent canister of the exhaust treatment system.

It is an aspect of an embodiment to define each of the first tier cutouts by an outer edge between adjacent arms, and the second tier of cut-outs defined by an inner edge proximate an end of each arm, four in the illustrated embodiment. The cutouts may take most any shape, but are semi-circular in some embodiments.

It is a further aspect that a distance from the center to a closest point of the first tier cut-outs is a first distance and the distance from the center to a closest point of the second tier cut-outs is a second distance, the first and second distances being different. The first distance is less than the second, by about half in a particular embodiment.

The surface of each arm is angled to create turbulent flow. In an embodiment, the surface is angled relative to a plane connecting the center and an outer edge of each arm.

These and other aspects of embodiments are described in the following detailed description and shown in the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of a vehicle after-treatment system illustrating an embodiment of the present NOx reduction system positioned within the vehicle exhaust gas;

FIG. 2 is a side cross-sectional view of the vehicle after-treatment system similar to that shown in FIG. 1, further illustrating exhaust gas flow, ammonia gas dispersion and mixing of the two;

FIG. 3 is a close-up of the upstream side of an embodiment of the NOx reduction system;

FIG. 4 is a close-up of an embodiment of the injector;

FIG. 5 is a perspective view of an embodiment of the ammonia injector;

FIGS. 6A-B are side views of an alternate embodiment of the ammonia injector;

FIG. 7 is a perspective view of an embodiment of the ammonia injector positioned upstream of an embodiment of the mixing plate;

FIG. 8 is a side view of an embodiment of the mixing plate;

FIG. 9 is a front perspective of the mixing plate shown in FIG. 9; and

FIG. 10 is a side view illustrating the use of the mixing plate to support the injector.

DETAILED DESCRIPTION

With reference to FIGS. 1-10, embodiments of a system and methods are described to one of skill in the relevant art. Generally speaking, a NOx reduction system, designated with the reference number 10 in the figures, typically works in conjunction with an exhaust gas after-treatment system 12 and comprises a mixing chamber 22, an injector 20 and a mixing plate 50. Typically, the reductant provided for use in the system 10 is carried on-board in canisters (not shown) which require periodic recharging. While embodiments using ammonia as the reductant are disclosed, embodiments disclosed herein are not so limited, and other reductants may be utilized instead of, or in addition to, ammonia for carrying out the embodiments disclosed and claimed herein. Examples of such other, or additional reductants include, but are not limited to, urea, ammonium carbamate, and hydrogen.

FIGS. 1 and 2 illustrate a vehicle exhaust after-treatment system 12 having, in downstream direction, an exhaust inlet 16, a diesel oxidation catalyst (DOC) canister 17, the NOx reduction device 10, a NOx particulate filter (NPF) canister 18, and an outlet 19. FIG. 2 further illustrates the exhaust stream flow before the NOx reduction device 10 (flow A), during mixing (flow B) and after the device 10 (flow C). Flow A is comprised entirely of engine exhaust gases, while the composition of flow B is (1) exhaust gases, (2) ammonia gas, and (3) a mixed gas, and flow C is comprised almost entirely of mixed gas.

FIG. 3 shows centered positioning of the injector 20 within the mixing chamber 22 (i.e., the space between the DOC and the NPF). Positioning the injector 20 in the chamber 22 center allows for optimum dispersion of the ammonia gas from a fixed, single, multi-port injector 20.

Referring to FIGS. 3-6, embodiments of the injector 20 are illustrated. Generally, the injector 20 comprises an inlet 24 which couples directly to an ammonia feed line 26 at one end and to the injector body 28 at the other end. The inlet 24 is on a back surface of the injector body 28, as illustrated in FIGS. 1 and 2. Alternatively, the inlet 24 may be positioned between two adjacent arms 30, as shown in FIG. 4. Multiple discharge ports 32 are used to disperse ammonia throughout the mixing chamber 22. In the embodiment of FIGS. 3-6, four discharge ports 32A-D are positioned one at the end of each of four arms 30A-D. As shown in FIGS. 3-5, the injector 20 is formed in the shape of a cross, separating the ports 32A-D by about 90 degrees one from another. A plurality of channels 34 within the injector 20 direct the ammonia gas from the inlet 24 to the discharge ports 32.

While other multi-port injector configurations are possible, the four-port cross-injector 20 shown has proven to be most effective at disbursing ammonia throughout the mixing chamber 22. The injector 20 is positioned substantially in the center of the mixing chamber 22 with the discharge ports 32 aimed in a direction perpendicular (or substantially perpendicular) to the exhaust stream flow.

In an alternate embodiments shown in FIGS. 6A-B, the injector discharge ports 32 are aimed directly upstream (FIG. 6A) or at some angle greater than zero incident to the exhaust stream (FIG. 6B) to disburse ammonia. However, such a configuration exposes the ports to plugging. Accordingly, to prevent plugging of the discharge ports 32 with exhaust particulates, shrouds 40 are used to shield each of the ports 32. The shrouds 40 are attached to the body 28 of the injector 20 and are conical in shape to minimize the creation of exhaust backflow. The number of shrouds 40 should correspond to the number of ports 32, but it may be conceivable to cover more than a single port with a shroud for some applications.

Another important aspect of the NOx reduction system 10, is the use of mixing plate 50. Referring to FIGS. 7-9, the mixing plate 50 is comprised of a multi-faced, multi-armed body 52, with at least two tiers of cutouts 54 dispersed about the circumference of the plate 50. The mixing plate 50 is positioned downstream of the injector 20, as shown in FIG. 1.

In the illustrated embodiment, the mixing plate body 52 has four arms 56 extending from the plate center 57. Each arm 56 has a surface or face 58 and is similarly angled or twisted to one side, much like a fan blade, as best shown in FIG. 8. The angled plate face 58 is used as a barrier region to deflect the gas streams, as shown in FIG. 3, and create turbulent flow to cause efficient mixing. Tabs 59 at the end of each arm 56, with reference to FIG. 9, provide a surface for attachment of the mixing plate 50 to the canister wall 62. Other attachment means may be equally suitable.

The cutouts 54 are considered to be two-tiered because of the distance each is from the plate center. The first tier cutouts 54A are positioned between adjacent arms 56 and extend closest to the plate center, while the second tier cutouts 54B are centered at the top of each arm 56 and are shorter. As a result, the mixing gases—i.e., exhaust gases and ammonia gas—are diverted laterally before passing the plate 50 into the NPF 18. Additional cutout tiers may be used if desired. Further, while the cutouts 54 are shown to be semi-circular, other shapes and sizes may be used to accomplish the desired distribution of gases within the mixing chamber 22.

Another function of the mixing plate 50 is as a support for the injector 20. As shown in FIG. 10, the ammonia feed line 26 may come into the mixing chamber 22 from downstream of the mixing plate 50 and then passes through the plate to position the injector 20 at the chamber center. The plate 50, which is secured at several points to the canister wall 62, stabilizes the injector 20, via the ammonia feed line, which is otherwise secured at a single point. 

What is claimed is:
 1. A mixing plate for use in a NOx reduction system, the mixing plate comprising: a plurality of arms each having a surface area and extending from a center of the plate; a barrier region, defined by the collective surface areas of the arms and substantially centered on the center, for diverting fluid flow outward; a first tier of cut-outs, each defined by an outer edge between adjacent arms; a second tier of cut-outs, each defined by an inner edge proximate an end of each arm; wherein a distance from the center to a closest point of the first tier cut-outs is a first distance and the distance from the center to a closest point of the second tier cut-outs is a second distance, the first and second distances being different, and the surface of each arm being angled relative to a plane connecting the center and an outer edge of each arm.
 2. The mixing plate of claim 1, wherein the number of arms is four.
 3. The mixing plate of claim 1, further comprising tabs extending from an end of each arm interspersed between adjacent first tier cut-outs and second tier cut outs.
 4. The mixing plate of claim 3, wherein the number of tabs is eight.
 5. The mixing plate of claim 3, wherein the tabs are substantially perpendicular to the surface of the arm from which it extends.
 6. The mixing plate of claim 1, wherein the first distance is less than the second distance.
 7. The mixing plate of claim 6, wherein the first distance is about half the second distance.
 8. The mixing plate of claim 1, wherein the first tier cut-outs are semi-circular.
 9. The mixing plate of claim 1, wherein the second tier cut-outs are semi-circular.
 10. A system for mixing a reductant with engine exhaust, the system comprising: an exhaust flow created by a vehicle engine; an injector positioned within the exhaust flow and having a plurality of ports for discharging reductant into the exhaust flow; a mixing plate positioned within the exhaust flow downstream of the injector and comprising: a plurality of arms each having a surface area and extending from a center of the plate; a barrier region, defined by the collective surface areas of the arms and substantially centered on the plate center, for diverting fluid flow outward; a first tier of cut-outs, each defined by an outer edge between adjacent arms; a second tier of cut-outs, each defined by an inner edge proximate an end of each arm; wherein a distance from the center to a closest point of first tier cut-outs is a first distance and the distance from the center to a closest point of the second tier cut-outs is a second distance, the first and second distances being different, and the surface of each arm being angled relative to a plane connecting the center and an outer edge of each arm; wherein each of the plurality of ports is aligned with each of the plurality of arms.
 11. The system of claim 10, wherein the injector is centered in the exhaust flow.
 12. The system of claim 10, wherein the injector discharges reductant into the exhaust flow to create an exhaust/reductant mixture.
 13. The system of claim 12, wherein the mixing plate creates tangential and circumferential flow in the exhaust/reductant mixture relative to the exhaust flow.
 14. The system of claim 10, wherein the number of arms on the mixing plate and the number of ports on the injector are four.
 15. The system of claim 10, further comprising tabs extending from an end of each arm of the mixing plate and interspersed between adjacent first tier cut-outs and second tier cut outs.
 16. The system of claim 15, wherein the number of tabs is eight.
 17. The system of claim 10, wherein the first distance is less than the second distance.
 18. The system of claim 17, wherein the first distance is about half the second distance. 